Light reflectors have long been used to bounce light off of a reflective surface. Light generally shines in all directions from a light source. However, if light shining in all directions from a light source is not useful, a reflective surface can be employed to reflect light towards a direction in which the light is useful. In this way, light reflectors increase the efficiency of a lamp or light source.
One general type of reflector comprises a concave reflector having a parabolic contour with respect to a focal point, so as to reflect frontwardly and along the lamp axis light emitted by a light source located at and near the focal point. The cross section of the reflector, perpendicular to the lamp axis, usually is circular with the diameter thereof varying with the distance from the focal point.
Another general type of reflector comprises a concave reflector having an ellipsoidal contour with respect to a focal point, so as to reflect frontwardly and along the lamp axis light emitted by a light source located at and near one of the ellipsoidal focal points to the second ellipsoidal focal point located frontwardly and determined by the size of the geometric ellipsoidal contour. The light leaving the ellipsoidal reflector usually passes through a gate and then enters into a series of lenses to more accurately control dispersion of the projected beam of light. The cross section of the reflector, perpendicular to the lamp axis, usually is circular with the diameter thereof varying with the distance from the focal point.
Additionally, a cone of light rays, originating from the light source, pass, unreflected, through the front of the reflector; the angle of this cone of rays being determined and defined by the front rim of the reflector. The more widely divergent light rays of the cone of rays, that is, the rays passing relatively nearer to the rim of the reflector, have such a large sideways component of direction so as to fall outside of the desired light pattern or gate and therefore are wasted.
The wasted, divergent light can be reduced, and the optical efficiency improved, by making the reflector deeper, that is longer, so that relatively more of the light is reflected in the desired direction and the cone of non reflected light is narrowed. However, there are practical limitations on increasing the depth of the reflector, such as cost, weight and awkwardness of use. Also, with a given maximum diameter as the reflector is made deeper, the focal point moves closer to the rear surface, which complicates positioning of the light source in reflector systems and if the light source is a filament inside a reflector lamp there is accelerated blackening of the nearby rear area of the reflector due to evaporation of the filament material (usually tungsten). This accelerated blackening in the reflector lamp can be alleviated by providing a concave recess at the rear portion of the reflector but has the drawback of reducing optical efficiency. In a reflector or reflector system, as the focal point moves closer to the rear surface, the percentage of reflected energy from the finite light source is compressed and packed much more tightly toward the center of the reflector and, as a result, the opening for the finite light source will remove an area of the reflector that would normally reflect a larger percentage of the light being generated than if it were a shallow reflector, thus reducing optical efficiency of the deep reflector system.
Additionally, it has now been found that as the parabolic or ellipsoidal contour of the reflector is made deeper and the focal point is moved closer to the rear of the reflector, the reflected light and heat from the light source is packed more tightly and reflected in a compressed narrower band at the center of the projected beam pattern or gate. This increase in light and heat energy is increased logarithmically as the reflector depth is increased in relation to the same width. This causes uneven projected beam patterns with concentrated areas know as hot spots in a parabolic reflector system or hot spots and uneven coverage of light causing shadows in the gate of an ellipsoidal reflector system. These compressed areas also concentrate heat at the center of the projected beam that can be very detrimental to parts of the illumination system and accessories used with these systems such as, but not limited to, color gel material, gobos, plastic lens, projection slides, and film used in motion picture projectors.